I went through something similar (though considerably less concerning) replacing a bunch of outlets in my house recently. I had wanted to replace these outlets for years since some of the receptacles were so loose, plugs would barely stay in. With the birth of my son in September, I finally...
To get cashback from Befrugal, you can only use coupon codes posted on the Befrugal site. This is stated in their terms and conditions. This happened to me once as well, before I (re)read the T&Cs.
Yeah, found them through this article: https://www.thisoldhouse.com/how-to/fixing-cracks-concrete
Didn't know anything about the company, but the product worked out well. If I found more cracks in my foundation, I'd use it again (no affiliation with the company).
I believe oilslick is referring to this product: https://www.radonseal.com/crack-injection/diy-injection.htm
I used Polygem, which seems to be pretty similar. For the fairly sizable crack in my foundation, which was letting in water whenever snow was melting or heavy rain, it worked well...